determine the rate of carbon dioxide exhalation while at rest

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					The SOTM LAB: B3                                                  11/23/99

Title of Lab: Carbon Dioxide Measurement
DEVELOPERS OF LAB: Darlene Brown JD810, Roger Norton JD829, Beverly Nostro
JD531, Patrick Ryan JD821, Frank Hess JD721, Merle Hess JD722, Elizabeth Shirley

     Since carbon dioxide measurement cannot be done directly, we have devised a
     mechanism for quantification of carbon dioxide output from a human under different
     conditions. The students will be directed to use laptops and probes to determine the rate
     of carbon dioxide exhalation while the student is at rest. Subsequently, the students will
     be asked to consider conditions that will change the CO2 measurements. They will state
     a problem, a hypothesis, design an experiment, carry out the experiment, and analyze
     their results.

        This lab can be used to reinforce the concepts of cellular respiration and breathing,
        which is covered in unit 2 of the Regents Biology Syllabus.

        pH in a swimming pool
        acid rain
        carbonic acid equilibrium
        exercise uses energy
        carbonation in liquids

        The pH probe bottle needs a cap for "storage" so it does not sit open on the lab table.
        Place several layers of paper towels under the beaker to absorb splashing when students
        are bubbling.

             Carbon dioxide exhaled through a straw into a beaker of water will combine
            with the water to form carbonic acid. Carbonic acid is a weak acid and will
            cause the water solution to become acidic. This increase in acidity can be
            measured by use of a pH probe and the results recorded on the computer. The
            students can relate the rate of carbon dioxide release by the rate of the change of
            pH. Comparing the rates of carbon dioxide exhaled under different conditions
            will result in identification of increases or decreases in respiration. As an
            enrichment activity, the pH of the solution can now be used in a series of

               chemical mathematics to figure out the volume of carbon dioxide that was

              1. Exhaled air contains only carbon dioxide.
                 Air contains nitrogen that is inert and therefore will be exhaled.
              2. Breathing and respiration are the same process.
                 Breathing is a physical process, respiration is a chemical one.
              3. Inhaled oxygen is converted into carbon dioxide.
                 Carbon dioxide results from the metabolism of glucose or some other organic
                 nutrient during cellular respiration.
              4. The difference between a pH of 3 and 5 is two single units of measure
                 Each pH unit is 10 times greater or lesser than the one next to it.

     1. To understand the importance of pH
     2. To compare the rates of carbon dioxide production during different activities
     3. To appreciate the use of technology in the field of science
     4. To learn science through inquiry

     Laptop computers                  interfaces and cables   surge protectors
     pH probes                         wash bottles
     Buffer solutions, pH 4 and 7      Kimwipes

       beakers: 4- 50ml, 1-600ml, 1-250ml, 1-1000ml
       stopwatch (clock with second hand)
       graduated cylinder - 500ml
       distilled water - several gallons
       paper towels
       ring stands and clamps

     Familiarize yourself with the computer program and probes.
     Soak the pH probes in distilled water for several hours or overnight
     Familiarize yourself with the safety precautions.
     Gather the necessary equipment and supplies.
    Copy student edition of lab (pages 4 & 5)
    Copy pre-lab exercise (page 3)


                                        Pre-lab Exercise
  1.    What is the chemical difference between pH 3 and pH 5?

  2.    What is meant by pH?

  3.    Explain respiration.

  4.    Explain breathing.

  5.    Briefly explain the chemical process between the time an individual breathes in and breathes

  6.    What gas(es) go in and what come out?

  7.    What processes occur in the cells?

  8.    What organelles produce the exhaled gases?

  9.    What happens to the exhaled air when you bubble it through the water?

  10.   From what chemical process does the exhaled air originate?

  11.   Neutrality on the pH scale is represented by what number?
  12.   Draw and label acidic, neutral, and alkaline on the pH scale indicating hyronium and hydroxyl

  13.   Can you tell the pH of a solution by its color and explain.

 Concept mapping terms
 respiration                                  breathing                    carbon dioxide
 oxygen                                       carbonic acid                acid
 base                                         log                          hydrogen ion

 OH-                           scale           7
 Neutral                       buffer          exhale
 Inhale                        excretion       volume
 cellular respiration          aerobic         anaerobic
 organelle                     mitochondrion

See Appendix A (page 11)

To determine the rate of carbon dioxide exhalation while at rest.

(Note: The Science Workshop program records and displays the pH of the solution. Since
carbon dioxide combines with water to form carbonic acid, the pH will indicate the amount of
carbon dioxide exhaled. The pH drops as the water contains more carbonic acid.)


        Part I - Computer Setup
        1. Connect the Science Workshop interface to the computer, turn on the interface, and
            then turn on the computer. Refer to separate sheet, if necessary.
        2. Connect the pH probe DIN plug into Analog Channel A on the interface.
        3. Open the Science Workshop program on the computer:
            a) Click the Zoom box or the Maximize button to change the experiment setup
                 window to full size.
             b) Click and drag the icon of the analog plug to Analog Channel A and release.
                This will cause a new screen to appear for the selection of the probe.
             c) Scroll to the pH probe. Double click on the pH probe. This places the pH
                sensor on the original screen (Experimental Setup Window) in a square box.
             d) Click onto and drag the graph icon from among the display options to the pH
                box. A choice box will appear. Click on pH, then click display and a graph will
             e) Click on graph display bar and drag the graph display to the bottom right of the
             f) Click onto and drag the digits icon from among the display options to the pH
             g) In the choice box, click on pH, then click display and a digits box will appear.
             h) Click on digits display bar and drag the digits display to an empty area on the

        Part II: Calibration of the pH sensor
        Note: If the sensors have not been soaked, calibration may not be possible.
        1. Gently blot the pH probe with Kim wipes.
        2. Double click on pH and this brings up the pH Analog Sensor Calibration screen.
        3. It is important to calibrate the pH probe. For calibration you will need distilled water
            and buffer solutions of pH 7 and 4. The probe must be kept moist at all times.
        4. Immerse the end of the pH probe in the pH 7 buffer solution.
        5. When the voltage displayed as the Cur Value: (current value) stabilizes, click on the
            READ button for the High Value: Then move the cursor to the High Value box and
            enter 7.0.
           (Note: Check pH of tap water. If near 7, it may be substituted for distilled water)

6. Thoroughly rinse the pH probe in distilled water, (using an empty beaker to catch the
   runoff), gently bot dry it with a Kim wipe and immerse the end of the probe in the
   pH 4 buffer solution.
7. When the voltage displayed as the Cur Value stabilizes, click on the READ button
   for the Low Value. Then move the cursor to the Low Value box and enter 4.0. Click
   on OK when finished. Now the calibration is complete.
   WARNING: If you quit the program and begin again, a new calibration must be

8. Thoroughly rinse the pH probe with distilled water and then place it back into
   the original beaker of distilled water.
9. On the left side of the screen is a box labeled Sampling Options. Click on this box to
   choose the correct frequency for sampling. Set "Periodic Sampling" for 2
   Seconds. Click on slow in the upper left corner and then set 2 S. Click OK at
   the bottom of the box.

Part III: The Experiment
The lab group consists of 2 - 4 students.

1. Using the graduated cylinder, measure 500 ml. of distilled water and pour it into the
   600 ml beaker
2. Set up the ring stand and attach the probe to the ring stand with the end of the probe
    in the beaker. See (diagram E). Place the beaker on multiple layers of paper
3. One student double click on the REC button in the main window.
4. Another student uses a straw to exhale into the water. Hold the straw between your
   fingers and keep your fingers around the probe. This will minimize splashing. See
   (diagram H). Continue this for two minutes. Your results will appear on the digits
   display and on the graph display.
5. Click STOP at the end of two minutes.
6. Run #1 will appear in the Data list in the experiment setup window. To observe
    results of this run, click on Run #1. You can then click on the Autoscale
    button to re-scale the graph to fit the data.
7. If possible, save to a disc and print a copy of the graph.
8. Using the graph, write out a data table of Time vs. pH (see sample)

     Diagram E

                                                                      Diagram H

After students have completed the “at rest” breathing rate experiment, have them discuss in their
lab groups the following question, “What condition can result in a change in the amount of CO2
produced in the basic experiment?”
Have groups make a list of factors that might result in a change. (Possible factors include:
exercise, weight (size) of person, sex of person, holding one’s breath for a while, re-breathing air
into a paper bag several times.

Have students select one factor that they would like to investigate and have them write a sentence
that will show the relationship between the factor and the rate of CO 2 exhalation.

     Questions to ask students:
         1. What is the variable that you are studying?
         2. How will you attempt to test the effects of this variable?
         3. What equipment do you need?
         4. What safety precautions must you be sure to follow in your experiment?

        Student groups prepare written experimental design

        CHECKPOINT (Teacher checks to see that students have answered questions

         1. Questions to ask students:
         2. What data do you plan to collect?
         3. What icons will you need to open on your laptop screen?
         4. Design an appropriate data table.
         5. What information will you be graphing?
         6. How do you plan to use the data collected to help you confirm or refute your

        Student groups complete written plan for investigation.

        CHECKPOINT (Teacher checks plans for feasibility.)

    Groups carry out their experiments using the written procedures they have developed.

        CHECKPOINT (Teacher monitors students’ investigations in progress.)


           As the teacher circulates among the groups, the following questions might be asked:
           Were there any surprises in your data?
           If yes, does this pose any new problems?
           Why do your two graphs look similar or different?
           Why do your data tables look similar or different?

        CHECKPOINT (Teacher checks students’ data.)

     Each group will present its findings to the entire class. They should be sure to include:

           The hypothesis
           An evaluation of the hypothesis
           Evidence to support the results of the investigation
           Comparison of preconceptions with the experimental conclusions

        As each group presents, it is responsible for convincing the other groups of the validity
        of its findings.

        The teacher may lead a discussion of how results relate to real world situations, as
        applicable. Some of these may include:

           pH in a swimming pool
           Acid rain
           Exercise uses energy
           Carbonation of liquids
           Carbonic acid equilibrium
           Use of technology in industry and research

     Have students retake the Pre-Lab Exercise. Compare pre-lab and post-lab responses.

     Submit lab report for evaluation

     See following rubric and rubric criteria sheets.

                           Carbon Dioxide Measurements

Examples of value points for each skill. Other suggestions may be better and may depend on
your own style. You may also use a non-graded scale.

Physically connects the components
  1.    connects no parts
  2.    connects computer and power pack
  3.    can connect computer, power and interface
  4.    connects all parts but can't trouble shoot
  5.    connects all parts and is able to trouble shoot problems

Operates the computer for setup
  1.   can't turn the computer on
  2.   opens program and is then clueless
  3.   follows directions for setup of software
  4.   aware of what he/she is doing with software
  5.   is able to troubleshoot software problems

Manipulation of sensor -software
  1.   sits and looks at the screen
  2.   able to start recording of data
  3.   can start and stop recording
  4.   knows how to use windows to show data
  5.   can do a run and restart for next run

Usage of multiple programs
  1.    no usage
  2.    can only use Science Workshop
  3.    can use Science Workshop and other program

Can print out important data
  1.    cannot turn the Printer on
  2.    turns printer on but cast operate-it
  3.    can only print one part of lab
  4.    can print lab data in one form (graph)
  5.    can print all lab data and WP lab report

Is able to evaluate the data
   1.     looks at the data and grins
   2.     can explain what happens in one trial
   3.     can explain data in multiple trials
   4.     can explain connections between two trials
   5.     can use data to explain human processes

Can explain the purpose of the lab
  1.    thinks the lab has to do with breathing
  2.    thinks the lab is to learn how to use a computer
  3.    thinks the lab is about exercise and rest
  4.    thinks the lab is about comparing rates
  5.    thinks the lab is about human variability

Can explain the sequences
  1.    does not know what a sequence is
  2.    cannot go beyond hooking up the hardware
  3.    can only explain software sequencing
  4.    can combine software and hardware
  5.    can go beyond components to lab exercise

Understands the limitations of the lab
  1.   there are no limitations
  2.   understands software limitations
  3.   understands variations in lab

Can enumerate sources of error
  1.   can not find any source of error
  2.   finds only superfluous sources of error
  3.   sophisticated experimental errors

Collaborates with partners for success
  1.    does not participate in lab
  2.    only wants to watch others
  3.    will only record data - not participate
  4.    will participate in the whole lab
  5.    takes leadership role in the group

Extrapolates the principle to real world
  1.    does not know what extrapolation means
  2.    provides erroneous extrapolation
  3.    can only provide extrapolation
  4.    can provide extrapolation & explanation
  5.    can provide evidence of multiple extrapolations

                             Carbon Dioxide Measurement

Period:           Date:

A. Physically connects the components                     1   2        3           4       5

B. Operates the computer for setup                        1   2       3        4           5

C. Manipulation of sensor software                        1       2       3            4       5

D. Usage of multiple programs                             1   2       3 4              5

E. Can Print out important data                           1       2       3            4       5

F. Is able to evaluate the data                           1       2       3            4       5

G. Can explain the purpose of the lab                     1       2       3            4       5

H. Can explain the sequences                              1       2       3            4       5

I. Understands the limitations of the lab                 1       2       3            4       5

J. Can enumerate sources of error                         1   2        3           4       5

K. Collaborates with partners for success                 1       2       3            4       5

L. Extrapolates the principle to real world               1       2       3            4       5

                                                  Appendix A

Questions the teacher may wish to ask the student to think about.
  Why doesn't the pH drop below 4.3
        Because carbonic acid and C02 and water reach equilibrium at pH of 4.3

    Explain why it does drop below 4.3 momentarily
        Because the reaction is pushed past equilibrium momentarily.

    Why is time important in this lab.
       Because time is used to measure the rate (speed) at which C02 is produced.

    Why is it necessary to start each trial with fresh water
       Because the previous water is no longer water. It contains carbonic acid and could
       tested with an indicator to prove it.

    Why was calibration necessary?
       In order to equate the pH of the water with the sensing equipment.

    What questions would you ask about this lab?
         The student may ask a variety of questions of a particular nature.

Common Misconceptions and Solutions

    Exhaled air contains only C02
         Air contains nitrogen that is inert, therefore will be exhaled as well

    Breathing and respiration confusion
        Breathing is a physical process, respiration a chemical one

    C02 combines with H20 to form carbonic acid not just bubbled out
         Can see the drop in pH on the graph

    Colorless water or carbonic acid looks the same
        Radioactive labeled oxygen doesn't show up in C02, but in water excreted

    Observation - they both look clear
        Can use indicators to show difference

    Oxygen is converted to carbon dioxide
        Explain the Electron transport system and Krebs cycle

    Concerning pH
        Use pH probe, graph, indicators show pH scale,

       *This material is based upon work supported by the National Science Foundation under Grant No.
       ES1 9618936. Any opinions, findings, and conclusions or recommendations expressed in this
       material are those of the author(s) and do not necessarily reflect the views of the National Science


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